Clinicopathological Analysis of 21 Thymic Neuroendocrine Tumors

Background: Thymic neuroendocrine carcinomas (NECs) are uncommon, for which there is no established information available because of a limited number of epidemiological study in Asia. Methods: We reviewed 21 cases of surgically resected thymic NECs, and evaluated their pathological and clinical features. Results: It showed male predominance (male/female ratio, 15/6) with wide age range from 20 to 72 years (mean age, 49 years). All 21 cases were divided into two types according to the World Health Organization criteria: atypical carcinoid (n = 18) and large cell NEC (n = 3). Three cases of atypical carcinoid (AC) were associated with ectopic Cushing's syndrome. All the patients (3/3) with large cell NEC (3/3) and 16.7% (3/18) of those with AC died of tumor progression. Common sites of metastasis included lung, lymph node, brain, lumbar spine, mediastinum, bone, and liver. Conclusions: In conclusion, thymic neuroendocrine tumors carry a poor prognosis. Regarding the tumor classification, our results showed that a vast majority of carcinoids in the thymus correspond to ACs. In addition, our results also indicate that typical carcinoid is a very rare entity. Some cases of AC exhibited a large size, solid pattern and they showed aggressive clinical behavior, which highlights the spectrum of histologic appearances of thymic NECs.